Power Catamarans

Power catamarans offer space, frugality, and both long-range and day sailing capabilities — what else sets them apart?

Power catamarans generally come in either planing or displacement versions. The former may have larger engines and handle in some ways like a monohull powerboat. Trawler versions use displacement to add stability and frugality, so make for ideal adventure vessels; or indeed party vessels because of vast, stable decks. Handling them is fairly easy in good conditions, but of course this changes with adverse weather.

Power catamaran design

Bridgedeck clearance is one of the most important design considerations. This is the gap between the deck and the water. Just think of the water tunnel between the hulls and consider how the water evacuates when a wave hits. Generally about one metre is ideal many builders don't manage this and of course overloading them further compromises this.

Topside profile is a key characteristic in handling and living on a power cat. The sleeker the lines, the less the drag but the downside is reduced volume inside. Sleeker hulls also sit much easier at anchor, rather than blunt shaped forward profiles often found on foreign imports.

Overloading is the way to kill a catamaran's performance, so adhering to the designer's weight limitations is important.

Fine entry bows reduce drag and enhance their famed frugality, but the downside is the lack of buoyancy.

Power catamaran characteristics

Catamarans are characterised by having two separate hulls joined by a deck, known as the nacelle. The wide beam created by a catamaran is both a blessing and curse, as experienced Kiwi catamaran designer Roger Hill told me: “Correct beam-to-length ratio is important (too much beam equals too much stability and a very uncomfortable motion in the ocean).”

Two engines are generally used on the modern power catamaran, so another reason for their relatively high expense. When offshore it's common practice so shut one down, once cruising speed is attained, so frugality is to the fore.

Redundancy is the big advantage with two separate powers plants, with their own fuel supply. Smaller vessels, like the versatile Aquila 36, use outboards, which free up space outside the hull and allow beach landings. Pod drives or sail drives are used on many major brands such as the Fountaine Pajots.

Handling a power catamaran

Twin engines, several metres apart means that power catamarans can be manoeuvred fairly easily by even the novice steerer. Planing models often use trim tabs and modern brands generally offer manual and automatic versions. Smaller planing ones can easily be trimmed by simply tilting their outboards, to optimise the ride and fuel efficiency.

Windage, created by the high topsides and vast flybridges, means that scenarios can become complicated and fraught in tight marina spaces. For example I witnessed a 50 foot catamaran being spun around right in front of me by a gust off the French coast because of the tunnel wind effect on the vessel. However, in most scenarios these boats that have adequately powered engines can be controlled. The large models, such as some big Lagoons have the option of a single bow thruster to compensate for the windage.  

Flybridge steering positions give complete visibility and are ideal for manoeuvring. But suffer from a lot of motion at sea, so a second steering position, or a simple autopilot control setup can help with this.

At speed, the motor catamaran is stable. Of course it can't lean into high speed turns like a monohull. One downside of this is larger turning circles but of course done without spilling your Gin&Tonic and completed very comfortably.

Hobby-horsing, is the violent motion suffered by some catamarans and occurs for a variety of reasons. Poor design, incorrect trim and inexperienced skippering are among the culprits. For example, certain sea states with a particular wave amplitude can set them off. Good design can help by centring all the weight (batteries, tankage, generators and so on) in the middle of the nacelle.

Slow speed handling is generally controlled by using both throttles to control the direction and as they are wide apart, the effect is pronounced. Also, turning the vessel in its own length is easily done by fore and aft movements of the throttles. However, as mentioned, windage can create leeway. The same principle applies when going astern, with judicious use of both levers.

Oncoming seas can pose a challenge because of the vast acreage of squared-off bow area. Traditional builders may use netted trampolines to minimise drag/impact but many choose solid GRP to give a monocoque structure to the vessel. This can create slamming below the hull and give an unpredictable motion which is dangerous for crew moving around on deck. Heavy seas may require fore-reaching which is slowly going forward at a slight angle to the growing waves. Bluewater sailors may deploy a sea anchor in storm conditions.

Running with the seas is typically the most popular scenario that cat cruisers seek out. It can be a very stable experience but waves can slam as they pass through the tunnel between the hulls. The main danger, like most vessels, is broaching. Often done by a sea going faster than the vessel and pushing it sideways to the oncoming wave. Going beyond the hull speed, can lead to losing control and broaching or even pitch-poling; yet slowing down can lead to being pooped. Experience and nimble throttle control is required in these challenging scenarios, as is putting the hulls at a slight angle to the following seas; increasing the effective length of the catamaran by presenting its diagonal distance.

Beam seas can often be taken well because of the vast beam of the catamaran which aids its overall stability. However, the beam means one hull will suddenly falls into the trough, causing a violent change of motion, so ensure all crew are secured.

Cruising on a power catamaran is popular in shoaling, sheltered waters where the main characteristics of the design comes to the fore. Places like the Gold Coast and behind the islands of northern Queensland are ideal powercat territory. Here the high costs of berthing one in a marina can be avoided and the long-range fuel capabilities enjoyed.